fix: inlineTokens rebuilds the reflink-mask preamble per call

src/Lexer.ts

@@ -306,14 +306,11 @@ export class _Lexer<ParserOutput = string, RendererOutput = string> {
     let maskedSrc = src;
 
     // Mask out reflinks
-    if (this.tokens.links) {
-      const links = Object.keys(this.tokens.links);
-      if (links.length > 0) {
-        maskedSrc = maskedSrc.replace(this.tokenizer.rules.inline.reflinkSearch, match0 =>
-          links.includes(match0.slice(match0.lastIndexOf('[') + 1, -1))
-            ? '[' + 'a'.repeat(match0.length - 2) + ']'
-            : match0);
-      }
+    if (this.tokens.links && src.includes('[')) {
+      maskedSrc = maskedSrc.replace(this.tokenizer.rules.inline.reflinkSearch, match0 =>
+        Object.hasOwn(this.tokens.links, match0.slice(match0.lastIndexOf('[') + 1, -1))
+          ? '[' + 'a'.repeat(match0.length - 2) + ']'
+          : match0);
     }
 
     // Mask out escaped characters

test/specs/redos/quadratic_footnote_defs.cjs

@@ -0,0 +1,17 @@
+// Regression: many reference definitions + references must not be quadratic.
+// Lexer.inlineTokens rebuilt its reflink-masking preamble on every call;
+// with n defs and n refs that took ~24s at n=13000 (exponent ~3).
+const n = 13000;
+let refs = '';
+const defs = [];
+const links = [];
+for (let i = 0; i < n; i++) {
+  refs += `[^${i}] `;
+  defs.push(`[^${i}]: x`);
+  links.push(`<a href="x">^${i}</a>`);
+}
+
+module.exports = {
+  markdown: `${refs}\n\n${defs.join('\n')}`,
+  html: `<p>${links.join(' ')}</p>\n`,
+};

test/specs/redos/quadratic_nested_reflink_defs.cjs

@@ -0,0 +1,14 @@
+// Regression: recursive link text containing '[' must not rebuild lookup state
+// for every reference when many link definitions are present.
+const n = 13000;
+const defs = ['[id]: /url'];
+const links = [];
+for (let i = 0; i < n; i++) {
+  defs.push(`[unused-${i}]: /${i}`);
+  links.push('<a href="/url">[x]</a>');
+}
+
+module.exports = {
+  markdown: `${'[[x]][id] '.repeat(n)}\n\n${defs.join('\n')}`,
+  html: `<p>${links.join(' ')}</p>\n`,
+};